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Monday, April 13, 2009

What are our muscles really doing when we pedal?

So my fit Studio is in a  Physical Therapy clinic, which makes sense, because I am a practicing PT.  My co-worker, and owner of the PT clinic, Rik is trained in a new biofeedback system.  Biofeedback uses electrode patches placed over the muscles to determine how much these muscles are working -- how much, how soon they kick in, how long they stay "on", how they "turn off", etc.  As you can imagine, this is highly useful with our clients.

So we decided to test a few cyclists and see what we came up with.  We could simultaneously use the Retul, to pick up movement imbalances and then cross reference with the biofeedback to try and figure out what the muscles on each side of the body were and were not doing.  We can even then use the biofeedback while the person pedals to "train" them what activating certain muscles at specific times "feels" like to help correct the underlying muscular problem.

First we have to test as many people as we can, to start to figure out common muscular patterns.  Hopefully we can figure out what is "normal" but if my line of work has taught me anything, it's that there aren't many "normals" out there.  That's why I think it's more likely we'll find common motor patterns that may not be symmetric, amongst many athletes.

Subject #1 : Me, 33 y/o, male, 5'10", 175#

I have a fairly symmetrical pedal stroke.  If I had to guess I would think that I am a bit right side dominant, and probably scoot off the right side of my saddle because of it.  But we don't have to guess, because here is a right and left Retul file from a recent test on myself:

Not bad.

Next was to hook up the biofeedback.  This involves placing small sticker-like electrodes strategically over the muscles you want to test.  Wires snap to the electrodes and run to a little processing unit that reminds me of a car radar detector.

The "radar detector" talks to the laptop via a BlueTooth connection -- the setup is pretty slick.

The software that Rik uses seems to have endless choices on how to set up the display screens so that you can simultaneously see what the
 different muscle groups are doing.

  When I was hooked up to the biofeedback unit we decided to test vastus lateralis (VL) (the quadricep or thigh muscle on the outside of the
 leg -- this tends to be very pronounced in cyclists), vastus medialis (VM) (quad to the inside just above the knee, and the hamstring.  We tested these muscles on both legs, so we could compare how much more the right or the left lateral quad was working, but we could also compare how much and when the medial vs. the lateral quad did work on the same side.  We could also compare this to how the hamstrings worked.

We tested all three muscle group -- VL, VM, hamstring -- on both legs, of course at 150 watts and at 215 watts.

The printout from the biofeedback looks like this:

The lines and squiggles at the top half of the page are usually in color, but they are a bit above what we want to get into here. 

Below are the printouts bottom half of the page.  The colum to focus on is the one that says "Mean" -- they are basically the normalized mA that the electrodes pick up from each of the

There are four sets of data:  comparing VMO/VL at 150 Watts, VMO/VL at 215 watts, VMO/hamstring at 150 watts, and VMO/hamstring at 215 watts.

VM/VL @ 150 watts

VM/VL @ 215 watts

VM/hamstring @150 watts

VM/hamstring @ 215 watts

As you can see from the sheets, my right quads (medial and lateral) both work more than the left at all wattages.  But when I increased from 150 watts to 215 watts my left quads increased their activity 18% while the right increased 23% (VL) and 29% (VM).

The next round of tests, comparing the VM to the hamstrings on both sides confirmed an 18% and 29% increase respectively for left and right for the VM when going from 150 watts to 215 watts.  The hamstrings, which overall, were not very active increased 31% on the right and 38% on the left; this increase on the left might make one think that the left "evens out" at higher wattage, but I think it is still a bigger issue: the right hamstring was more active at 150 than the left was at 215.  The fact that the starting point for the left hamstring was so bad made it's improvement seem more drastic.

What did we learn?
I think this first round of tests is encouraging and shows that we can, with good effect correlate what our mechanics are like (from the Retul data) and what the muscles themselves are doing.  We should be able to explain why a cyclist may pedal with an asymmetry and whether it is due to a poor motor plan or if it has more structural origins.

I think we can safely say that one of the main reason that I sit a bit skewed on the saddle is because my pedal stroke's motor plan has a significant emphasis on my dominant right leg.  I think with more data we will see that my current pedal stroke is poor in the efficiency category because I have not been riding as much  lately and I am getting a very small contribution from the hamstring muscles.  I am not "pedaling ellipses" but rather more up and down (and definitely more down than up).


I have a theory as well about the activation of our quadriceps when we pedal that has to do with left and right efficiency.  I believe I am more coordinated (because pedaling is a coordinated task) on my right leg -- it's clear my hamstring are more active on the right and help to smooth out my pedal stroke.  I am also more skilled at one leg pedaling drills on my right leg -- less "clunking" through the stroke and better cadence.  

I think, based on some of the muscle activation graphs that I saw for me (and they would have been difficult to post here -- sorry), that our more efficient leg will see the quads activate later and relax earlier than the non-dominant side.  So the non-dominant side will have a more consistent or longer activation patter than the dominant side.  

This to me seemed counter-intuitive at first, but after some thought I realized that because my dominant side hamstring were activating better, they would inhibit the quads sooner since the load was now taken up by this new group of muscles -- the more "normal" or efficient pedal stroke.  The dominant side could more accurately and quickly kick itself on and off in time with my cadence and when it kicked on it could fire more motor units more quickly.  I think this would have implications, of course, on negative torque values (when your quads are still pushing down on the pedal after it has passed the dead bottom center position and therefore exerting negative torque or power) but also in terms of fatigue.  The non-dominant quad is staying "on" longer, even when it shouldn't and wastes unnecessary effort -- it fatigues quicker even though it is adding less to the overall workload.

Anyway, I should have more data coming this weekend and next week with a  few more guinea pigs so stay tuned.


  1. This is a great blog. I like how you really put the science behind bike fitting. I've had a bike fitting before but definitely not to this degree. Any chance you know of a knowledgeable bike fitter in Southern California? You are a little far to get to but after reading your articles, it may be worth the trip.

  2. Thanks for reading. I don't know any of the bike fitters in southern Cal firsthand, and I'm always wary about recommending anyone unless I am sure they put as much into their fit process as I do. I guess I'm just particular.
    We have great riding (road and mountain) out here, so if you plan a road trip give me a ring and we'll get you set up. Thanks again. --John